1. Field of the Invention
The present invention relates to an elastic wave control element using a piezoelectric material which can be inserted into a propagation path for elastic waves or installed in an oscillator to allow the elastic waves in a selected frequency or in a selected frequency band to be damped, reflected or transmitted.
2. Description of the Prior Art
As methods for absorbing elastic waves such as a sound or vibration which is propagated through an elastic substance, there are sound absorption by glass-wool or the like and vibration damping using a damper or the like. In these methods, the energy of the elastic waves is changed to thermal energy through an elastic loss such as that from use of a sound absorption material and a damper. Therefore, the elastic waves are damped by consuming the thermal energy.
Further, as methods for reflecting the elastic waves, there are sound insulation by concrete or the like, vibration damping using a spring, and the like. Usually, in elastic waves which are propagated through gas or liquid, a reflection effect can be increased by using a large mass or elastic constant. On the other hand, in elastic waves which are propagated through a solid body, vibration transmission rate can be decreased by using a small elastic constant.
In this manner, a method in which a different kind of material is inserted into a medium which propagates the elastic waves or installed in an elastic substance to allow the elastic waves to be absorbed or reflected is called passive control. In this method, a damping factor, a reflection factor, and a transmission factor (i.e. vibration transmission rate) depend on the elastic constant and the elastic loss of the different kind of material.
On the other hand, an active control method which involves a sensor, an operation part, a controller and an actuator has also been used recently. This active control method is characterized in that, when the sensor senses the elastic waves, the actuator is driven through the operation part and the controller to damp the elastic waves.
However, in the passive control method, the damping factor, the reflection factor, the transmission factor (i.e. the vibration transmission rate), and their frequency characteristics are mainly determined by the size, shape, elastic constant, and elastic loss of the different kinds of materials. Accordingly, those characteristics depend on temperature and pressure, but could not be changed artificially.
Further, in the active control method, a complicated system and control method are required to obtain sufficient effect.
On the other hand, if an element which can freely change the damping factor, the reflection factor, the transmission factor (i.e. the vibration transmission rate) was available and wherein those frequency characteristics can be realized using a simple system, it is considered that the element will be widely applicable in many different fields because the elastic wave can be freely damped, reflected, or transmitted in a selective frequency band.
It is an object of the present invention to overcome the above-mentioned problems found in the prior art and to provide an elastic wave control element using a piezoelectric material of a simple construction which can easily change a damping factor, a reflection factor, a transmission factor (i.e. a vibration transmission rate), and their frequency characteristics, and which can not only damp, reflect or transmit elastic waves in a specified frequency or a selected frequency band, but also compensate those temperature characteristics.
To attain the object above, according to a first aspect of the invention, an elastic wave control element is provided which is inserted into transmission path for the elastic waves and installed in an oscillator to allow the elastic waves in a selected frequency to be damped, reflected, or transmitted, and comprising a piezoelectric material provided with a pair of electrodes between which a negative capacitance circuit is connected to allow the capacitance and loss factor of the negative capacitance circuit and their frequency characteristics to be changed selectively, and to allow the loss factor of the negative capacitance circuit in a selected frequency to be matched with a dielectric loss factor of the piezoelectric material.
According to a second aspect of the invention, an elastic wave control element is provided which is inserted into a propagation path for elastic waves or installed in an oscillator to allow the elastic waves in a selected frequency band to be damped, reflected or transmitted, and comprising a piezoelectric material provided with a pair of electrodes between which a negative capacitance circuit is connected to allow the capacitance and loss factor of the negative capacitance circuit and their frequency characteristics and temperature characteristics to be changed selectively and to allow frequency characteristics and temperature characteristics of an absolute value of the capacitance and the loss factor of the negative capacitance circuit to be matched with frequency characteristics and temperature characteristics of the capacitance and the loss factor of the piezoelectric material in a selected frequency band and temperature range.
According to a third aspect of the invention, an elastic wave control element is provided which is inserted in a propagation path for elastic waves or installed in an oscillator to allow the elastic waves in a selected frequency band to be damped, reflected, or transmitted, and comprising a piezoelectric element provided with a pair of electrodes between which a negative capacitance circuit is connected to allow the capacitance and loss factor of the negative capacitance circuit and their frequency characteristics to be changed selectively, and to allow the frequency characteristics of an absolute value of the capacitance and the loss factor of the negative capacitance circuit to be matched with the frequency characteristics of capacitance and the loss factor of the piezoelectric material in a selected frequency band.
According to a fourth aspect of the invention, an elastic wave control element is provided which is inserted into a propagation path for elastic waves and installed in an oscillator to allow the elastic waves in a selected frequency or frequency band to be damped, reflected or transmitted, and comprising a piezoelectric material provided with a pair of electrodes between which a negative capacitance circuit is connected to allow capacitance and loss factor of the negative capacitance circuit and their temperature characteristics to be changed selectively, and to allow temperature characteristics of an absolute value of the capacitance and the loss factor of the negative capacitance circuit to be matched with temperature characteristics of the capacitance and the loss factor of the piezoelectric material in a selected temperature range.
According to a fifth aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above, in which an element of the negative capacitance circuit, for determining a loss factor, is made of the same material as the piezoelectric material.
According to a sixth aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above, in which an element, for determining a loss factor, among elements forming the negative capacitance circuit forms a network using at least one of a resistor, a condenser, and a coil.
According to a seventh aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above is constructed such that at least one of the elements forming the network is made of the same material as the piezoelectric material.
According to an eighth aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above is constructed such that the resistor of the network is variable to allow the frequency characteristics of the capacitance and loss factor of the negative capacitance circuit to be variable.
According to a ninth aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above, further comprises combined elements formed by connecting three elements to the piezoelectric material. The combined elements are connected to the negative capacitance circuit, and the three combined elements form a network, and include at least one of a resistor, a condenser, and a coil.
According to a tenth aspect of the invention, the elastic wave control element using the piezoelectric material as discussed above is construced such that one of the three combined elements is opened, or at least one of the other two elements is short-circuited.